1. Field of the Invention
The invention relates to a terminal apparatus for an electrolytic device such as a battery, and more particularly relates to a terminal apparatus installed in a battery container wall, compressibly set against the opening in the battery container wall so as to seal against gas and/or electrolyte leakage.
2. General State of the Art
A recurring problem in the battery industry is that of being able to seal a battery terminal where it leaves the battery container. Ideally, a batter terminal should be able to seal against leakage of electrolyte and/or gases contained within the battery, whose escape would be undesirable.
One common approach is to cast an alloy lead bushing with multiple latitude rings and then mold the plastic of a battery case around the lead bushing. The intent of this approach is to try to get the plastic to shrink around the lead to maintain a seal between the lead and the plastic. However, thermal cycling will allow the plastic to creep in relation to the lead, due to the differences in coefficients of thermal expansion of the plastic and the metal. Thus, the seal will frequently fail, allowing capillary seepage at the interface of the plastic and lead.
Another approach to the problem has been to take a premolded alloy lead bushing and subsequently roll form or swage the bushing into a cavity in the plastic. Initially, this results in a tight, intimate sealing surface between the lead and the plastic. However, as time goes on, thermal cycling will again cause the opposing sealing surfaces of the metal and the plastic to creep relative to one another, again eventually allowing capillary seepage to occur at the interface.
Moreover, the designs described above are intended to operate with very little pressure differential across the seal. Battery systems exist which will exert considerably more pressure across the seal. For example, sealed lead-acid, starved electrolyte recombinant systems, such as are manufactured by Gates Energy Products of Denver, Colo., operate over a pressure differential range of anywhere from partial vacuum to over 1.3 atmospheres. In a situation such as this, a much more efficient seal is required between the lead and the plastic at the terminal interface to permit prolonged use of such a battery without failure due to capillary seepage. Battery terminals using previous approaches in the art are only marginally acceptable in this application, and a need exists for a type of battery terminal which is more successful at withstanding these relatively higher working pressures and extending the overall field life of this type of battery. Of course, if a new type of battery terminal were to be developed which could successfully withstand these higher working pressures and increase the life of this kind of battery, then it should also prove itself to be superior in performance in those battery applications requiring lower working pressures.
The present invention meets this need and overcomes the shortcomings of the prior work in the field. One of the objects of the invention is to produce a battery terminal capable of handling battery pressure differentials across terminal seals ranging from partial vacuum to several atmospheres. Another object of the invention is to produce a battery terminal that would be highly resistant to capillary seepage after repeated thermal cycling. Yet another object of the present invention is to provide a method of manufacturing such battery terminals in a relatively simple manufacturing method that would not require overly sophisticated manufacturing equipment or inordinately high amounts of capital investment.
Metals can be plastically deformed by various processes such as extrusion, drawing, rolling or swaging, A plastically deformed metal becomes stronger and the conventional index of plastic deformation is called cold work. Cold work is the amount of plastic strain introduced during processing of a metal. The increase in hardness resulting from plastic deformation during cold work is called strain hardening. Both the tensile strength and the yield strength of a metal are increased, and accompany this increasing hardness. In the operation known as swaging, metal is force-shaped to the contours of a tool. With regard to the present invention, a swaging operation occurs using an essentially cylindrical, tapered punch, which is forced down through the center of two annular bushings whose internal diameters are less than the external diameter of the punch, resulting in the metal being forced to expand radially and thereby affect work hardening.